A wired telecommunication system such as, for example, a Private Branch Exchange (PBX) has attracted widespread use for business communications because of its flexibility of allowing one to design specific services in accordance with one's business needs. Nevertheless, the equipment with which the PBX users communicate are traditional telephones which are hardwired to the PBX switch. This undesirably limits the mobility of the user who is tethered by the cord connecting the handset of a telephone to its fixed base-unit. Although the traditional telephones can be replaced with cordless telephones to increase the mobility, this replacement, however, does not provide a desirable solution because the portable handset of a cordless telephone must interact with the fixed base unit associated therewith. This being so, as the distance between the portable handset and the base unit increases, the signals to and from the handset are accordingly attenuated. In addition, significant interference is caused by the signals from other cordless telephones which are also connected to the PBX switch. As such, the mobility gained by using a cordless telephone is not only limited, but also results in a compromise of signal quality.
Attempts have been made to solve the above-identified problems. One such attempt involves the use of a pico-cellular communications system such as described in the publication by D. .ANG.kerberg, "Properties of a TDMA Pico Cellular Office Communication system," IEEE ICC 1989, pages 186-191. In such a system, fixed base units are connected to a centralized system manager to provide a transceiving function for the various different pico-cell sites. The system users are supplied with portable handsets which can interact with any one of the fixed base units. As a mobile handset moves from a pico-cell site of a first base unit to another pico-cell site of a second base unit, the provision of the transceiving function is switched from the first to the second base unit under the control of a system manager. Although this switching scheme is intended to solve the signal attenuation problem, it does, however, still require relative high transmission power. The fact that the transmitted signals contain relatively high power may preclude such system from operating in certain radio-frequency bands. Moreover, although this system manages to eliminate the above-noted interference by using a time-division-multiple-access (TDMA) scheme (i.e., each portable handset can only transmit and receive signals during its preassigned time slots), the received signals in this system are corrupted by another type of degradation, namely, multipath distortion. Such distortion occurs when various mutually delayed version of the signal travel along various paths of different lengths. Furthermore, to achieve a significant capacity a substantial spectrum allocation may be required.
Accordingly, a need exists for a wireless telecommunication system which does not have the above noted defects.